Catégories : environnement montagne, expéditions

Type d'article : collaboratif (CC by-sa)

What is high altitude?

Good question! In this book, we are talking about going from close to sea level to anywhere above 2,000m. Our bodies are used to working at home. When we go higher they need to adapt. Altitude starts to have an effect around 1,500 - 2,000m. The body starts to behave slightly differently as it tries to make up for the change in oxygen levels. Go up too fast to about 2,500m and altitude illnesses are common.
Given enough time to adapt, most people can adjust to altitudes between 5,000m (Everest base camp) and 5,500m. Above 5,500m few people can adjust any more. Health and ability then get worse. So what’s different about travel at altitude? The main difference is that as you go higher the air pressure gets lower (the air gets ‘thinner’), and this means for any single breath that you take there will be less oxygen for your body. Oxygen is needed to give you the energy to move, but is also needed simply to keep your body alive - for your brain and digestion to work, for healing cuts, and all those normal things your body does without you knowing about it. As your body gets less oxygen it adapts. You breathe faster and deeper. It makes more red cells to carry more oxygen in the blood. Changes take time to happen. If you go slowly you should stay healthy. Go up too fast and you risk suffering from altitude related illnesses, such as Acute Mountain Sickness (AMS).

Where in the world is high ?

There are many places in the world where you can go to high altitude. You can choose to, by going on a trekking or climbing holiday. It may come as more of a surprise when using high ski runs, driving or cycling over high passes or even flying into towns and cities which are high - like La Paz. Each high altitude area has its own problems. Before travelling you should find out more about where you are going.

ASIA

The most popular areas for high altitude trekking and climbing are in this part of the world.

From Nepal, Pakistan or India it is usually possible to make a gradual ascent into the mountains - ideally avoiding the highest landing strips. 84% of people flying in to the Hotel Everest View (3,860m) suffered AMS. A gradual ascent to the Tibetan plateau is impossible, so AMS symptoms must be carefully monitored and exercise kept to a minimum until acclimatised.

Acclimatisation

When the body slowly adapts to lower oxygen levels the process is called acclimatisation. Different people acclimatise at different speeds, so no rule works for everyone, but there are good guidelines.
Over 3,000m go up slowly, sleeping no more than 300m higher at the end of each day. Going higher during the day is ok as long as you go down to sleep (“walk high - sleep low”). If you go up higher and can’t descend - take a rest day to allow your body time to ‘catch up’.
For your group:
This may seem very slow, and some people will comfortably be able to go up much faster, but in a group someone will always be the slowest to acclimatise - and the timetable should be made to keep them healthy. A rest day scheduled after every 2 to 3 days will also help.
Driving or flying to high altitude means more people will suffer from AMS. It is really sensible to find out about the height of your planned route before you travel. Better still, make a drawing to show the height that you will sleep at each night. If you don’t know - ask. There’s no better way to spot the days which are likely to cause altitude illness.

The effects of altitude

Most people going high have to deal with altitude related illnesses. Dealt with correctly, they are unlikely to be a major problem. Dealt with incorrectly they can be disastrous - spoiling the trip for the person who is ill and those with them. Being honest about how you feel each day can make a difference, and knowing what’s happening to you could save your life.
Some very strange things can happen to your body when you go high! Most people who have been to altitude can tell you about having headaches, being out of breath, sleeping badly and not feeling hungry. These are symptoms of AMS. AMS is uncomfortable, not life threatening. If the AMS symptoms become severe and you keep going higher - fluid in the brain (High Altitude Cerebral Oedema - HACE) or fluid in the lungs (High Altitude Pulmonary Oedema - HAPE) can happen and these can kill you very quickly.
What people don’t know about is that you’ll need to pee more, your balance may become unsteady, your eyesight could change and your nails will grow differently.
I hope the following pages will tell you about some of the things you may experience and how best to deal with them. Some are mainly about comfort, but some can lead to long term damage to health or death. Finding out about what your body is doing as it goes higher is fascinating and can become part of the fun of travel! In fact, when you think how clever your body is at dealing with such big changes, you may even want to know more!

Acute Moutain Sickness (AMS)

The common symptoms for AMS are:

• Headache.
• Nausea (feeling sick).
• Vomiting (being sick).
• Fatigue (feeling tired).
• Poor appetite (not hungry).
• Dizziness.
• Sleep disturbance

A simple scorecard everyone should have, and one must keep a check of their scores twice a day. It’s good if everyone logs how they feel while travelling - and is honest with others in the group. Everyone can help make decisions - to go up, to have a rest day, or to go down. As a group, everyone’s health and happiness is equally important.
Hiding illness or pushing someone on could be fatal. Some people just seem to acclimatise slowly, and need to take things more gently. If you are unfit, it doesn’t mean you are more likely to suffer, but overdoing it might be risky. If you are unused to exercise, feeling tired while trekking is not surprising. Similarly if you are sleeping in a tent every night and are not used to it, your sleep may be poor. The food may also be very different.

The most important thing is: are the symptoms getting better or worse? If you think you are getting worse - walk down (at least 500 to 1,000m lower for sleeping). Give your body extra time to acclimatise. Don’t leave this decision until it’s too late.

The brain

The brain is affected by altitude because it needs a good supply of oxygen and may swell causing pressure.
High Altitude Cerebral Oedema (HACE) is caused by brain swelling and can kill very quickly if not treated. Some people feel no effects. Others may suffer any (or all) of the following: Headaches - very common at altitude, especially if you suffer headaches or migraine at home.
Loss of balance - co-ordination and balance may be affected. Older people and those who are acclimatised feel less effect. ‘Clumsiness’ and bad judgements increase the risk of accidents.
Mood changes - on a ‘trip of a lifetime’ there will be good days and bad days. Bad days can trigger disappointment and depression. Be prepared for mood swings!
AMS / HACE - see other pages.
Stroke - developing sight or speech problems and / or a weak arm, leg or face are signs of a stroke. (Some migraine sufferers have similar effects during an ‘aura’).

Hace

The main signs:
* Severe headache.
* Become clumsy.
* Act differently - unhelpful, violent, lazy.
* May have bad, non-stop vomiting.
* Blurred vision.
* See, hear, feel, smell odd things.
* Confused.
* Reduced consciousness.

Can they:

• Touch nose with index finger with eyes closed? Repeat rapidly.
• Walk heel to toe in a straight line?
• Stand upright, with eyes shut and arms folded?
• Do simple mental maths?

If not able to do or have difficulty doing any of the above, suspect HACE.
HACE can develop very quickly with no other problems or can follow AMS and HAPE.
What to do:

• Stay with the person at all times - do not leave them on their own. • Descend now - not later or in the morning.
• Sit them upright and keep warm.
• Give oxygen via cylinder or pressure bag if you have it.
• Give dexamethasone if you have it.
• Give acetazolomide if you have it.
• If really unable to descend - prolonged use of a pressure bag may be needed.

Consequence if ignored:
Loss of consciousness - confusion, drowsiness. Reduced breathing.
DEATH.
In serious cases death can occur within as little as an hour of symptoms being noticed.
Remember it is possible to have AMS, HACE and HAPE at the same time.
DESCEND DESCEND DESCEND DESCEND

Hape

The main signs:
* Trouble breathing.
* Tired & weary.
* Coughing.
* Froth and later blood in spit.
* Lips, tongue, nails become blue.

HAPE can develop in 1-2 hours or over several days and even when descending.

What to check for:

• Has there been recent ascent?
• Does it take a long time to get breath back after exercise?
• Are they breathless when resting?
• Is the breathing rate increasing?
• Can ‘wet’ / crackling sound be heard in chest? Put ear to back below shoulder blades.

What to do:
* Stay with the person at all times - do not leave them on their own. • Descend now - not later or in the morning.
* Sit upright and keep warm.
* Give oxygen via cylinder or pressure bag if you have it.
* Give nifedipine if you have it.
* Give acetazolomide if you have it.
* If really unable to descend - prolonged use of a pressure bag may be needed.

Consequence if ignored:
Breathing stops. DEATH.

In serious cases death can occur within as little as an hour of symptoms being noticed.
Remember it is possible to have AMS, HACE and HAPE at the same time.
DESCEND DESCEND DESCEND DESCEND.

Oxygen

The lack of oxygen causes many high altitude illnesses, the only real way to fix the problem is to get more oxygen. This can be done simply and sensibly by DESCENDING, or if this is impossible there are two ways to get more oxygen at altitude.

(1) From an oxygen bottle

Oxygen cylinders can be fitted with a face mask. The person needing oxygen simply puts on the mask and breathes in the oxygen, mixed with some of the surrounding air. If using a ‘constant flow’ kit (oxygen flowing all the time) at 2 litres per minute, a bottle containing 300litres will last 2 to 3 hours. If using a ‘demand flow’ kit (oxygen flows only when breathing in), the same bottle may last 6 to 9 hours.

(2) Inside a pressure bag

Those suffering from AMS, HAPE or HACE can be placed inside a ‘bag’, known as a Portable Altitude Chamber, Certec or ‘Gamow Bag’. The bag is ‘pumped up’ to increase the pressure inside - so the oxygen breathed is like that 2,000m lower. The person should stay inside for 1 hour but may need several hours. Lifting the head end may help with breathing. Although these bags can be a life-saver, there are problems:

• Hard to talk to the person inside
• An unconscious person needs someone inside to monitor them.
• They can damage the eardrums
• The air inside needs changing.
• Recovery is often short-lived.

WHAT TO DO IN AN EMERGENCY

Whatever the case, the most important thing is not to panic. The following points are aimed at helping you to deal with an emergency.

• Make sure everyone is safe - yourself, any casualties, the rest of the group. If one person has hypothermia, the chances are others may have it too.
• Move to somewhere safe if you have to. Do not become another casualty.
• Have one person in charge.

• Collect the information you need. Use ‘ETHANE’ as a guide.

  • Exact location.
  • Type of incident.
  • Hazards to rescuers
  • Access to the incident
  • Number of injured / ill
  • Equipment required.

• Communicate. The sooner you call for help, the better. Radios and telephones may not work in the mountains. Give your location first (so they know where the problem is). Be accurate.

• Treat casualties as best you can. Prioritise care based on how bad each injury is. Basic first aid is OK. Simple splinting and kind words can go a long way.
• Make evacuation plans-local transport, carry or helicopter.
• Keep everyone warm and safe until help arrives - it could be minutes, hours or days.

Recommended reading

• The High Altitude Medicine Handbook, by Drs Pollard & Murdoch Bugs,
• Bites, and Bowels, by Dr Wilson-Howarth
• Altitude Illness: Prevention & Treatment, by Dr Stephen Bezruchka
• Pocket First Aid and Wilderness Medicine, by Drs Jim Duff and Peter Gormley